This invention relates generally to electric motor drive arrangements, and more particularly to a DC shunt propulsion motor which is supplied from an electrical energy accumulator, illustratively a battery, wherein the armature of the motor is connected to the energy accumulator, and the field winding of the motor is connected to the energy accumulator via an electronic DC control element having a current control device for controlling the speed of the motor. A transmission having a variable reduction ratio is interposed between the motor and a drive axle.
DC shunt traction motors which receive electrical energy from an energy accumulator, such as a battery, are known and used in vehicles. In addition to drive control apparatus, there must further be provided a charging device which is either stationary or on the vehicle. The advantage of utilizing existing electrical infrastructure, such as 16 ampere outlets of a 220 volt supply network, is best achieved if the charging device is arranged on the vehicle.
An electric drive having a DC shunt traction motor supplied from a battery is described in German Reference DE-OS No. 24 12 416. In this known arrangement, the speed of the motor can be controlled by means of an electronic DC control element which operates as a chopper. The traction motor is provided with an armature winding which is connected to the battery in an essentially direct manner. Speed is controlled only via the field winding of the traction motor, which is connected to the battery via the electronic DC control element. The DC control element is provided with a current controller having an actual-value input which receives a signal proportional to the armature current. At a reference input of the current controller is provided a signal proportional to the excursion of a foot pedal. A transmission having variable reduction gear ratio is interposed between the output shaft of the motor and the drive shaft of the electric drive arrangement.
The use of a DC control element, such as a chopper, arranged in the armature circuit for charging the battery is known from German Reference DE-OS No. 27 02 276. In this further known arrangement, a controller sets the motor current simultaneously with the charging current, and is associated with the DC control element. In this known arrangement, however, a targeted division of the total current into a predetermined motor current and a desired battery charging current is not possible. If the motor is switched off, only current control is provided for the charging of the battery, thereby permitting overcharging and gassing of the battery.
It is, therefore, an object of this invention to provide a DC control element for controlling the charging of the energy source in addition to, but independently of, the speed control.